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110 Physics Developments in Modern Physics Contact Information Class homepage on classes*v2 server or go directly to: http://star.physics.yale.edu/~harris/physics_110/ Professor Harris' contact info John Harris (203) 432-6106 john.harris@yale.edu Teaching assistants Christine Nattrass christine.nattrass@yale.edu Matt Phillips matthew.phillips@yale.edu Announcements Pick up: Electronic Polling Devices (at Bass Library Desk) Homework assignment Problem Set 1 due Wednesday Jan. 23 For those not in class on Monday Pickup syllabus Questions on any points of syllabus or class concept? Optional discussion session (Tuesdays, starts next week) Test - Music Selection Which song would you like to hear? a. Walk into the Sun Dirty Vegas b. Cold Crossfade c. Dani California Red Hot Chili Peppers d. Alive Pearl Jam e. Vertigo U2 42% 24% 18% 13% 3% C c. ro D ... an iC al if o rn d .. .A liv e P ea e. .. V er ti g o U 2 in to t. . a. W al k b .C o ld Today's Lesson Scientific Method (from Chapter 1) Describing Motion (Chapter 2) 1-dimensional motion Vectors Graphing motion Speed, velocity, acceleration Scientific Method Scientific Method: (method effective at gaining, organizing and applying knowledge) 1. Observation "or recognize a problem" 2. Develop hypothesis "make educated guess" [a scientific hypothesis must be testable!] 3. Predict consequences of hypothesis Cycle - a way to test & refine 4. Test hypothesis with experiments theories 5. Form general rule that organizes hypothesis, prediction, outcome into a theory Scientific method is a guide, but sometimes - trial and error! Advances in science.... (an example follows) observation - what do you see? generalization/discussion hypothesis - how do you explain this? theory - how do you test this? What is a fact? always true? general agreement? Falling Objects tennis ball + piece of paper Better yet - Penny and Feather Tube Experiment 1.) Observation as above 2.) Hypotheses same as above 3.) How do you test this? Concept Question It is often difficult to distinguish scientific explanations of common events from other kinds of explanations (superstition, prejudice, magic, etc.). Which of the following best helps identify a scientific explanation? 1. The explanation violates our intuition. 2. We can test the explanation by comparing its predictions to measurement results. 3. The explanation changes according to the observer. 4. The explanation relies on local folklore. 94% 0% 3% 3% ex p la n at i.. W e ca n te st t. T . h e ex p la n at T i.. h e ex p la n at io ... T h e Concept Question The key distinction between science and religion is: 1. Truth. 2. Simplicity. 3. Testability. 4. God. 86% 3% S im p li ci ty . T ru th . 11% 0% T es ta b ili ty . G o d . Concept Question Which of these is a scientific hypothesis? 1. Atoms are the smallest particle of matter. 2. Space is permeated with an undetectable essence. 3. Albert Einstein is the greatest physicist of the 20th century. 4. All of the above. 5. None of the above. 63% 24% 8% 3% 3% 1. A to m s ar 2. e S t. p . ac e is 3. p ... A lb er t E in 4. st A e. ll . o f th e a. 5. .. N o n e o f th ... Concept Question Review Which of these is a scientific hypothesis? 1. Atoms are the smallest particle of matter. 2. Space is permeated with an undetectable essence. 3. Albert Einstein is the greatest physicist of the 20th century. 4. All of the above. 5. None of the above. Only 1 is scientific, it is testable. It is not only capable of being proven wrong, it is wrong! 2 has no test for wrongness. 3 has no test to be able to prove it either. Beware of pseudoscience! Chapter 2 Describing Motion Many things around us are in motion: birds, planets, cars, aircraft, . . speed = distance traveled in an interval of time (v = d/t) After 1 sec. After 2 sec. After 3 sec. After 4 sec. 0 10 m 20 m 30 m 40 m "Constant speed" of 10 m/s Normally, e.g. in a trip, your speed is not constant - you speed up and slow down. - v changes total traveled distance in a trip total time of trip "average speed" v= "instantaneous speed" is the reading on your speedometer at any designated time ( i.e. how fast you are going at that instant in time). Concept Question Jessie starts at rest and runs towards Daniel. The dots in the diagram below represent Jessie's position at 0.1 second intervals. A B C . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. Which diagram could represent Jessie's initial motion? 1. Diagram A 2. Diagram B 3. Diagram C 4. More than one diagram 5. None of them 79% 13% 3% 5% 0% 1. D ia g ra m 2. A D ia g ra m 3. B D ia 4. g ra M m o re C th an 5. ... N o n e o f th em "direction of travel" is important: "velocity" is a vector quantity describes how fast an object is moving & its direction of motion. (velocity speed & direction) Velocity constant, average, instantaneous velocity (ala speed but with direction) Cars going through a curve: speed of A = speed of B velocity of A velocity of B (Directions are different) B A Graphing Motion (1d) Describe the motion! distance time Slope of graphs?: larger d/t (velocity) slope higher the speed! (i.e. magnitude of velocity) Concept Question A train car moves along a long straight track. The graph shows the position as a function of time for this train. The graph shows that the train: 1. speeds up all the time. 2. slows down all the time. 3. speeds up part of the time and slows down part of the time. 4. moves at constant velocity. al .. 71% 21% 5% a. p .. . c. .. at 3% u p 1. sp ee d s 3. sp ee d s d o w n u p 2. sl o w s 4. m o ve s Vectors Things fall down Compasses point north . . (have a direction!) A vector is a mathematical construct describing a quantity (e.g. distance, velocity, . . . ) linked to a direction of space. Vectors are denoted by either d (i.e. boldface) or d (i.e. with an arrow over it) Boston d N.Y. vector distance d = 200 miles to the northeast. Vectors and Vector Addition vector a quantity with a magnitude and a direction examples of vector quantities: velocity, displacement, accelerations, force, momentum, . . . for vectors: direction is essential! e.g.) velocity of 100 mph due east 100 mph due north. scalar quantities: direction not essential e.g.) mass, volume, temperature Addition of vectors: A + B = C C B A Se pp eA C! dix en draw to scale and place tail to head. if more than 2 vectors added, draw them all before taking the sum. Subtraction of vectors: A - B = C B A -B C Take opposite direction of B then add (-B) to A and get C. (X,Y) components of a vector: y A Ay x Ax v/t Graphing Motion (1d) Describe the motion! distance time velocity (speed) Average v vf time Slope of graphs?: larger d/t (velocity) slope higher velocity! larger v/t (acceleration) slope more acceleration! 1 -D M o tio n e x a m p le - s p e e d o m e te r If v e lo c ity c h a n g e s r a p id ly, th e n B IG - a c c e le r a tio n !..... If v e lo c ity c h a n g e s s lo w ly, th e n s m a ll a c c e le r a tio n !..... If v e lo c ity = c o n s ta n t a c c e le r a tio n = 0 If a c c e le r a tio n is s u c h th a t th e s p e e d o m e te r m o v e s w ith a c o n s ta n t s p e e d , th e a c c e le ra tio n is u n ifo r m o r c o n s ta n t. A v e r a g e a c c e le r a tio n : a = fin a l s p e e d - in itia l s p e e d e la p s e d tim e 0 -5 0 k m /h in 5 s e c o n d s 2 a = 5 0 k m /h = 1 h r X 1 0 0 0 m = 2 .7 8 m /s 5 s 3600s 1 km Concept Question A car going around a curve at a constant speed accelerates! (its direction of velocity is changing) A A' The slope of the curve in the distance vs. time graph for a car's motion gives: 1. the car's speed. 2. the car's acceleration. 3. the car's average velocity. 4. the car's instantaneous velocity. distance 60% time 27% 7% ac ... 7% in .. . c ar 's s. .. c ar 's c ar 's 3. th e c ar 's 1. th e 2. th e 4. th e a. ..

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